1A type of plaster composed of ground gypsum, typically used in sculpture or for whitewashing walls. Also in figurative contexts. Compare "gesso". Chiefly US in later use.
2In sherry-making: a coarse powder made from gypsum (or occasionally from chalk-rich soil), traditionally added to grapes before crushing, mainly to acidify the must by the release of tartaric acid.
Mid 16th century; earliest use found in 2nd Baron Berners (c1467–1533), soldier, diplomat, and translator. From Spanish yeso, †yesso gypsum from classical Latin gypsum.